Hello, List of Similarities Both words describe a lack of tension or tightness. Both can be used to describe a lack of effort or productivity. Both can be used to describe a relaxed or lenient attitude. What is the difference? Usage: Lax is more commonly used to describe a lenient attitude towards rules or standards, while slack is more commonly used to describe a lack of effort or productivity. Physicality: Lax is more commonly used to describe a loose or weak physical condition, while slack is more commonly used to describe a loose or hanging physical object or material. Connotation: Lax has a more negative connotation, implying a lack of responsibility or carelessness, while slack can have a neutral or slightly negative connotation, implying a temporary or fixable situation. Based on this, She was staring into space, her mouth lax. The rope suddenly went slack. Hope this helps!